Posterior sinus of the middle ear.

OBJECTIVES

This study defines the anatomy of the posterior sinus of the middle ear and its relationship with the sinus tympani.

METHODS

Fifty-one temporal bone plugs harvested from human cadavers were studied. The depth and width of the posterior sinus, its relationship to surrounding structures, and the structure that separates it from the sinus tympani were studied.

RESULTS

The posterior sinus, positioned just posterior to the oval window, was 1 mm or less in depth, and the width of the opening 1.5 mm or less. A ridge of bone from the floor of the middle ear separated the posterior sinus from the sinus tympani in 82% of specimens. In 10% a sheet of bone separated the two sinuses, and in 8% the sinus tympani and posterior sinus formed one confluent recess.

CONCLUSIONS

This is the first study that describes the anatomy of the posterior sinus of the middle ear. This sinus is separated from the more inferiorly located sinus tympani by a ridge of bone, not by the ponticulus as was previously thought, and it is no larger than 1 mm in depth and 1.5 mm in width. The results from this study give the otologic surgeon knowledge of middle ear anatomy that he or she can use when removing cholesteatoma, granulation tissue, or retracted epithelium from the posterior tympanum.